The present invention relates to fluorescence analyzers and, more particularly, to flourescence detectors wherein the excitation radiation emanates from one focal line of an ellipsoidal cylinder and the sample is located at the other focal line.
As discussed in "Fluorescence Analysis of Picloliter Samples", Edmond A. Mroz and Claude Lechene, Analytical Biochemistry 102, 90-96 (1980), biochemical analysis of very small samples--on the order of picoliters--is required in both basic and applied sciences of cell biology. As explained, many attempts to analyze such samples have been tried, and many of these attempts have used microfluorescence methods. These methods have limitations, however, in the compounds that can be analyzed and the ease with which assays can be performed. The apparatus disclosed in the above-referenced article is a fluorometer chamber, created optically by using a capillary tube as a flow cell and a microscope-fluorometer to excite fluorescence in and to record fluorescence from a constant region within the capillary. Excitation radiation is directed transverse to the capillary tube and fluorescent radiation is similarly collected transverse to the capillary tube.
Such an apparatus has inherent problems in that the exitation radiation is not efficiently delivered to the sample volume because it is directed transverse to the capillary tube and, consequently, passes through only a small portion of the sample volume in the capillary tube. Further, the fluorescent radiation cannot be efficiently collected and delivered to a detector. The cumulative loss of excitation and fluorescent radiation results in an instrument having greatly reduced sensitivity.